IP addresses are our unique identifiers on the global Internet. They have parallels to the physical addresses we use for our mail. When we wish to send a letter, we post the letter to the known address of the recipient and we include our return address so the recipient knows where to send the reply to. IP addresses work in much the same way. When our computer system wishes to send information to a remote computer system, a message is sent to the known IP of that remote system and our own IP is included so the remote system knows where to send the reply to. IP addresses can be categorised in two ways: static and dynamic. Static addresses are those where the computer system retains one or more for permanent use. Dynamic addresses are assigned as and when requested. For example, your broadband connection at home may have a dynamic address. This may change periodically, such as when your broadband router needs to renegotiate the connection after a reboot. IP addresses do not have a direct relationship with the physical location of the devices using them. When groups of addresses are handed out, they are generally allocated to an individual geographical area. However these areas are large and determining a more precise location is not inherently available from the details of the allocation databases.